Structure-based redesign of GST A2-2 for enhanced catalytic efficiency with azathioprine

Glutathione transferase (GST) A2-2 is the most efficient human enzyme in the biotransformation of the prodrug azathioprine (Aza). The activation of Aza has therapeutic potential for possible use of GSTs in targeted enzyme-prodrug treatment of diseases. Based on the assumed catalytic mechanism and computational docking of Aza to the active site of the enzyme, active-site residues were selected for construction of focused mutant libraries, which were thereafter screened for Aza activity. Mutants with elevated Aza activity were identified, DNA sequenced, and the proteins purified. The two most active mutants showed up to 70-fold higher catalytic efficiency than the parental GST A2-2. The structure of the most active triple mutant (L107G/L108D/F222H) enzyme was determined by X-ray crystallography demonstrating significant changes in the topography of the active site facilitating productive binding of Aza as a substrate.     

Synthetic studies with the brevicidine and laterocidine lipopeptide antibiotics including analogues with enhanced properties and in vivo efficacy

Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both in vitro assays and in vivo infection models.

Convenient solid-phase approaches are described for the synthesis of brevicidine and laterocidine. Also reported are novel analogues including a laterocidine variant with enhanced hydrolytic stability and potent in vivo antibacterial activity.     

Ta3N5 nanoparticles with enhanced photocatalytic efficiency under visible light irradiation

Nanocrystalline Ta(3)N(5) particles with a surface area of more than 33 m(2)/g were synthesized by nitridation of nanosized Ta(2)O(5) particles using NH(3) as the reactant gas. It was found that nanocrystalline Ta(2)O(5) was converted into Ta(3)N(5) completely (by X-ray diffraction, XRD) at 700 degrees C within 5.0 h, which was much lower than the temperature 900 degrees C for the complete nitridation of micrometer-sized Ta(2)O(5) powder. The oxide precursor and the resulting nitride were characterized by XRD analysis, transmission electron microscopy, UV-vis diffuse reflectance spectra, and BET surface area techniques. The nitrogen contents in the prepared Ta(3)N(5) powders were quantitatively determined with a CHN elemental analyzer. Nanocrystalline Ta(3)N(5) showed an absorption edge of around 600 nm, and Ta(3)N(5) in the size of about 26 nm exhibited a blue shift of 15 nm in the adsorption edge. The photocatalytic activity of the prepared Ta(3)N(5) under UV-vis and visible light irradiation was compared to that of nanocrystalline TiO(2-x)N(x) using the photocatalytic degradation of methylene blue (MB) as a model reaction. The Ta(3)N(5) nanoparticles showed the significantly enhanced photocatalytic activity for the degradation of MB in comparison with the larger-sized Ta(3)N(5). Moreover, the nanocrystalline Ta(3)N(5) showed much higher photocatalytic activity under visible light irradiation compared with TiO(2-x)N(x) in the same size.     

Macromolecular salen catalyst with largely enhanced catalytic activity

A dinuclear copper(II) Schiff-base complex was immobilized in a poly(acrylate) matrix by emulsion polymerization. The spheric microbeads were used for aerobic catalytic oxidation of 3,5-di-tert-butylcatechol into 3,5-di-tert-butylquinone in methanol at ambient temperature to study the contribution of the macromolecular matrix to the overall rate acceleration of the reaction. The polymeric catalyst catalyzes the oxidation about 1 order of magnitude faster (kcat/knon = 470,000) than its low molecular weight analogue (kcat/knon = 60,000).     

TiO2 nanotube fabrication with highly exposed (001) facets for enhanced conversion efficiency of solar cells

We demonstrate that the use of poly(vinyl pyrrolidone) (PVP) and acetic acid during the synthesis of TiO(2) nanotubes may result in the synthesis of single-crystal-like anatase TiO(2) with a mainly exposed and chemically active (001) facet. An enhancement in the overall conversion efficiency of dye-sensitized solar cells was observed in a photoanode consisting of TiO(2) single-crystal-like anatase exposed (001) facets.     

Evidence of the electronic factor for the highly enantioselective catalytic efficiency of Cinchona-derived phase-transfer catalysts

[structure: see text] The Cinchona alkaloid-derived quaternary ammonium salts containing 2'-N-oxypyridine and 2'-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H(2)O via hydrogen bonding leading to high enantioselectivity (97 approximately >99% ee), which provides evidence of an electronic factor for the high enantioselective catalytic efficiency in phase-transfer alkylation.     

3-Methyl-2,3-dihydrobenzothiazoles as reducing agent. Dye enhanced photoreactions.

Various types of electron deficient saturated carbon atoms are reduced in a visible light initiated process by N-alkyl-2,3-dihydrobenzothiazoles; these reactions are accelerated in the presence of Ru(bipy)₃Cl₂. The same ring system can act as an enolate carrier under electrophilic conditions.     

Controllable preparation of highly dispersed TiO2 nanoparticles for enhanced catalytic oxidation of dibenzothiophene in fuels

The aggregation of nanoparticle catalysts is one of the main problems in catalytic reactions. In this study, a series of TiO₂ nanoparticle catalysts with various dispersions were prepared and applied in the catalytic oxidation of dibenzothiophene (DBT) systems. Compositions and structures of the as‐prepared samples were analyzed by means of wide‐angle X‐ray diffraction, Raman and X‐ray photoelectron spectroscopies. The dispersions of TiO₂ nanoparticles were controlled by calcining at various temperatures and verified using transmission electron microscopy. It was found that the activities of TiO₂ nanoparticles in the catalytic oxidation of DBT were positively correlated with the dispersions. TiO₂ nanoparticles calcined at 500 °C (500‐TiO₂) showed the best catalytic activity and the oxidation of DBT reached 99.8% under mild conditions. Based on the results of GC–MS analysis, radical trapping experiments and electron spin resonance spectra, ^?O₂^? radicals were proved to be the main active species in the oxidation process, and a mechanism is proposed. Meanwhile, the recycling performance of 500‐TiO₂ was investigated, and no obvious decrease was observed after six recycles.     

Smart paper transformer: new insight for enhanced catalytic efficiency and reusability of noble metal nanocatalysts

Although noble metal nanocatalysts show superior performance to conventional catalysts, they can be problematic when balancing catalytic efficiency and reusability. In order to address this dilemma, we developed a smart paper transformer (s-PAT) to support nanocatalysts, based on easy phase conversion between paper and pulp, for the first time. The pulp phase was used to maintain the high catalytic efficiency of the nanocatalysts and the transformation to paper enabled their high reusability. Herein, as an example of smart paper transformers, a novel chromatography paper-supported Au nanosponge (AuNS/pulp) catalyst was developed through a simple water-based preparation process for the successful reduction of p-nitrophenol to demonstrate the high catalytic efficiency and reusability of the noble metal nanocatalyst/pulp system. The composition, structure, and morphology of the AuNS/pulp catalyst were characterized by XRD, TGA, FE-SEM, ICP, TEM, FT-IR, and XPS. The AuNS/pulp catalyst was transformed into the pulp phase during the catalytic reaction and into the paper phase to recover the catalysts after use. Owing to this smart switching of physical morphology, the AuNS/pulp catalyst was dispersed more evenly in the solution. Therefore, it exhibited excellent catalytic performance for p-nitrophenol reduction. Under optimal conditions, the conversion rate of p-nitrophenol reached nearly 100% within 6 min and the k value of AuNS/pulp (0.0106 s⁻¹) was more than twice that of a traditional chromatography paper-based catalyst (0.0048 s⁻¹). Additionally, it exhibited outstanding reusability and could maintain its high catalytic efficiency even after fifteen recycling runs. Accordingly, the unique phase switching of this smart paper transformer enables Au nanosponge to transform into a highly efficient and cost-effective multifunctional catalyst. The paper transformer can support various nanocatalysts for a wide range of applications, thus providing a new insight into maintaining both high catalytic efficiency and reusability of nanocatalysts in the fields of environmental catalysis and nanomaterials.

A smart paper transformer supported nanocatalyst platform is developed based on the facile phase conversion between paper and pulp for both high-efficiency and high-reusability catalysis, with wide applications demonstrated by using Au nanosponge.     

In situ Sn-doped WO3 films with enhanced photoelectrochemical performance for reducing CO2 into formic acid

Journal of Solid State Electrochemistry - We report exploiting effective Sn incorporation to enhance the photoelectrochemical activity of WO3 plate films, applied as photoanodes for...     

Design of Pd{111}-TiO_2 interface for enhanced catalytic efficiency towards formic acid decomposition

Supports are commonly implemented in the industrial application of heterogeneous catalysts to improve the stability and recyclability of catalysts.The supported catalysts often show the enhanced activity and selectivity in various catalytic reactions.However,the specific contributions of electronic and steric effects to a catalytic system often remain elusive due to the lack of well-defined model systems.In this work,two types of uniform Pd nanocrystals covered by{111}facets in tetrahedral and octahedral shapes,respectively,are synthesized with identical chemical environment and loaded on Ti O_2supports to form hybrid structures(Pd{111}-Ti O_2)towards the application of formic acid decomposition.Our observation suggests that the polarization effect at the interface of Pd-Ti O_2enhances its activity in formic acid decomposition.Moreover,the Pd tetrahedrons-Ti O_2hybrid structure whose Pd{111}-Ti O_2interface possesses a larger angle shows higher catalytic activity,owing to the reduced steric effect as compared to Pd octahedrons-Ti O_2.This study reveals the nature of interface effects in formic acid decomposition,and provides a guidance for the related catalyst design.     

Automated modular preparative HPLC-MS purification laboratory with enhanced efficiency

Automated parallel synthesis as tool to increase productivity in chemical synthesis is well-established. However, even more time-consuming than the synthesis process is the following purification of the resulting crude products. To enhance efficiency of the lead optimization process at Bayer CropScience, a high-throughput HPLC/MS-laboratory for the purification of up to 48 crude products per day in the range of 200-400 mg each in one injection per sample has been set up. The use of Covaris technology for HPLC sample preparation, automated aliquotation during fractionation, and a novel evaporation process by combination with freeze-drying are new key technologies applied successfully for the first time in this purification unit facilitating to achieve the targeted efficiency. The whole process is supported by a specially designed IT-landscape covering each step of the workflow. Both the technical instruments used within the laboratory and the workflow and IT platform are described in this article.     

Heterogeneous Au-Pt nanostructures with enhanced catalytic activity toward oxygen reduction

Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.     

Copper nanoparticles modified silicon nanowires with enhanced cross-coupling catalytic ability

Copper nanoparticles modified silicon nanowires show enhanced catalytic activity for the coupling reaction of benzene halides (iodobenzene, bromobenzene, and chlorobenzene) and aniline.     

Light-responsive threadlike micelles as drag reducing fluids with enhanced heat-transfer capabilities

Drag-reducing (DR) surfactant fluids based on threadlike micelles are known to suffer from poor heat-transfer capabilities. Accordingly, the use of these fluids is limited to recirculating systems in which heat exchange is not important. Here, we show for the first time that light-responsive threadlike micelles can offer a potential solution to the above problem. The fluids studied here are composed of the cationic surfactant Ethoquad O/12 PG (EO12) and the sodium salt of trans-ortho-methoxycinnamic acid (OMCA). Initially, these fluids contain numerous threadlike micelles and, in turn, are strongly viscoelastic and effective at reducing drag (up to 75% DR). Upon exposure to UV light, OMCA is photoisomerized from trans to cis. This causes the micelles to shorten considerably, as confirmed by cryo-transmission electron microscopy (cryo-TEM). Because of the absence of long micelles, the UV-irradiated fluid shows lower viscoelasticity and much lower DR properties; however, its heat-transfer properties are considerably superior to the initial fluid. Thus, our study highlights the potential of switching off the DR (and in turn enhancing heat-transfer) at the inlet of a heat exchanger in a recirculating system. While the fluids studied here are not photoreversible, an extension of the above concept would be to subsequently switch on the DR again at the exit of the heat exchanger, thus ensuring an ideal combination of DR and heat-transfer properties.     

Cage-shaped borate esters with enhanced Lewis acidity and catalytic activity

[structure: see text] A cage shape causes high Lewis acidity and catalytic activity on boron. Borate esters that have cage-shaped ligands have accessible LUMO with lower eigenvalues than normal open-shaped borate esters. A large dihedral angle at C-O-B-O in cage-shaped borate esters induces less overlap between p-orbitals on O and B. The hetero-Diels-Alder reaction is effectively catalyzed by the cage-shaped borate, although the open-shaped borate does not act as a catalyst.     

Hydrothermally stable ordered mesoporous titanosilicates with highly active catalytic sites

Mesoporous titanosilicates (MTS-9) are successfully prepared in strong acidic media by a two-step synthesis. MTS-9 has an ordered hexagonal structure and exhibits superior hydrothermal stability and high catalytic activity for the oxidation of the small molecules of phenol and styrene and also of the bulky molecule of trimethylphenol.     

Immobilization of copper nanoparticles on WO3 with enhanced catalytic activity for the synthesis of 1,2,3-triazoles

In this study, a heterogeneous catalyst based on copper nanoparticles immobilized on metal oxide, WO₃, was fabricated using an impregnation method as an easy and straightforward nanoparticle synthesis strategy. The successful synthesis of the nanocatalyst was confirmed using various spectroscopic techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microscopy. The catalytic performance of the well-characterized material was evaluated through the azide–alkyne cycloaddition reaction (click reaction) in the aqueous medium. To optimize reaction conditions, different reaction parameters such as nanocatalyst amount, reaction time, temperature, and solvents were studied. Experimental results showed that as-prepared nanocatalyst (Cu/WO₃) could act as an effective and reusable heterogeneous catalyst in water for the synthesis of 1,2,3-triazoles in good-to-excellent yields. In addition, Cu/WO₃ has some advantages such as simple preparation procedure, easy separation, and recyclability for three runs with no remarkable loss of catalytic activity, which is essential from a catalytic application point of view.